Railway traffic controlling apparatus



Sept. 29, 1942. A. e. WILLIAMSON ETAL 3 9 RAILWAY TRAFFIC CONTROLLINGAPiPARATUS Filed Dec. 5, l941 3 Sheets-Sheet l Means ZNVFNTOHS Apba Gwzllzkzmsozz and Azga G. wz'llz amspn J QR THE/[Z ATTUR/VEY Sept. 29,1942. A. e. WILLIAMSON ET AL 2,297,119

RAILWAY TRAFFIC CONTROLLING APPARATUS Filed Dec. 5, 1941 3 Sheets-Sheet2 IP II Patented Sept. 29, 1942 UNITED STATES PATENT OFFIC RAILWAYTRAFFIC APPARATUS CONTROLLING Application December 5, 1941, Serial No.421,764

Claims. (Cl. 246-63) Our invention relates to railway trafilccontrolling apparatus, and more particularly to train carried traincontrol apparatus responsive to coded energy.

Coded energy is used in railway traffic controlling apparatus forgoverning train carried train control apparatus and wayside traingoverning signals, and when thus used such energy is supplied across thetrack rails at the exit end of a track section so that current flows inthe rails in series to energize a track relay connected acros the railsat the entrance end of the section when the section is unoccupied and toinductively energize a train carried receiver when such train travelsthe section in the normal direction of traflic. The coding is generallyeffected by periodically interrupting the supply circuit at apreselected code rate and a plurality of different rates are provided toreflect a plurality of different traffic conditions, the rates of 180,120 and 75 interruptions per minute being those generally employed toreflect clear, approach-medium and approach traffic conditions,respectively. The track relay governs Wayside signals according to thecode rate at which it is energized, while the energy picked up by thetrain carried receiver is decoded and used to operate a cab signal orother train control device according to the code rate of the energy thuspicked up.

Track sections are of a length predetermined in part according tobraking distance required for trains. The braking distance requireddepends upon the maximum permissible speed and the class of equipment.The high speeds prescribed for present day traffic require relativelylong braking distances and hence a relatively long track section if atrain is to be brought from maximum speed to a stop in a single tracksection. For this reason track sections of the order of 11,000 feet inlength are desirable Where high train speeds prevail. Broken railprotection is also an essential feature in such railway trafficcontrolling apparatus, and a single track circuit for a track section of11,000 feet in length provides satisfactory broken rail protection onlywhen either alternating current of a relatively low frequency or directcurrent is used. Thus some signal systems use coded direct current whichassures satisfactory broken rail protection and which can be obtainedfrom local batteries without expensive transmission lines.

Each code cycle of frequency codes of the type here involved consists ofan on and an off period. That is, each code cycle includes an on periodduring which current flows and an off period during which no currentflows. The on and of! code periods may be of substantially equaldurations. However, it has been proposed to make the on period short ascompared to the oil period. This latter form of coding is advantageouswhen direct current is used because it conserves the output of thecurrent source, which is ordinarily a battery. On the other hand, thestandard form of decoding apparatus used in railway traffic controllingapparatus of the type here involved is most satisfactorily operated inresponse to substantially equal on and off periods of operation of thecode following relay.

Furthermore, when coded direct current is used difliculty may beexperienced in the control of train carried apparatus because of thepossible energization of the train carried receiver by so calledmagnetized spots of the track rails. Such magnetized rail spots occur atrandom and act to induce electromotive forces in a train carriedreceiver as the train moves over such magnetized spots.

The direct current for such coded track circuit current is ordinarilyobtained from a battery, there being one battery usually provided foreach track section, and hence it is advantageous that the energy outputbe held at a low level, and to accomplish this result the train carriedapparatus must be effectively controlled by a relatively low inducedelectromotive force.

Because of these various conditions imposed upon railway traificcontrolling apparatus of the class herein contemplated, a feature of ourinvention is the provision of a novel and improved organization ofrailway traffic controlling apparatus which is effectively responsive tocoded energy.

Another feature of our invention i the provision of a novel and improvedorganization of train carried train control apparatus responsive tocoded direct current.

Still another feature of our invention is the provision of train carriedtrain control apparatus incorporating a novel and improved receiving andamplifying means which is effectively excited only by time spacedelectromotive forces derived from the two track rails alternately.

Again, a feature of our invention is the provision of novel traincarried train control apparatus of the type here involved wherewith codedistortion is avoided and substantially equal on and off periods areefiected for operating a decoding means, notwithstanding the controlimpulses of current may be of short duration as compared to the durationbetween successive impulses.

Furthermore, a feature of our invention is the provision of traincarried train control apparatus that is simple and of low cost, andwhich is effectively controlled by coded track circuit current of arelatively low energy level.

Other features, advantages and objects of our invention will appear asthe specification progresses.

The above features, advantages and objects of our invention are obtainedby providing on a train adapted to travel a track section whose railsare provided with coded direct current, a novel two-channel receivingand amplifying means and a decoding and signaling means. Each channel ofthe receiving and amplifying means comprises an inductor mounted on thetrain in advance of the leading pair of wheels and a gas filled orcontrolled ionization type of electron tube. The inductor of the firstchannel is mounted over one rail, and is connected to the grid circuitof the tube of the first channel, while the inductor of the secondchannel is mounted over the other rail and connected to the grid circuitof the second channel tube. .Each of the tubes is provided with a platecircult including a source of direct current which is of a voltageinsufficient to normally fire the tube but is sumcient to cause the tubeto become fired when a predetermined control electromotive force of theproper polarity is applied to the grid of the tube. The grid losescontrol when the tube once is fired and the tube can be extinguishedonly by either a decrease of plate voltage or a plate voltage of thereverse polarity for an interval at least equal to the deionization timeof the tube. The two receiving channels are inter-related for only onechannel to be onerative at a time and for the two channels to bealternately operative. This alternate operation is accomplished byproviding circuit connections for the inductors which permit thepredetermined control electromotive forces to be applied first to onetube and then to the other, and by interconnecting the plate circuits ofthe tube through an extinguishing device, such as a condenser, which ischarged when either tube is fired at a polarity such that when thesecond tube is fired the condenser discharges through the tubes inseries in a direction that extinguishes the first fired tube leavingsuch first tube in condition to be refired by the next controlelectromotive force. Thus a first control electromotive force is pickedup from a first one of the rails to fire the tube of a first one of thereceiving channels, a second control electromotive force is picked upfrom the second rail to fire the tube of the second receiving channel.and when the second channel tube is fired. the first channel tube isimmediately extin uished by the condenser and made ready to be refiredby the third control electromotive force which must be received from thefirst track rail. In other words, a first effective control electromotve force is picked up from one rail and the next effective controlelectromotive force is picked up from the other rail and such back andforth action of the control electromotive forces from one rail to theother is required for effective operation of the train carriedapparatus. An electromot ve force picked up at random due to a manetized rail spot is ineffective to exert a control on a receivingchannel unless such stray electromot ve force occurs just at a time thechannel menuated with the rail on which such magnetized snot occurs isat the moment conditioned to receive a control electromotive force andthe stray electromotive force is of proper polarity, and under suchcircumstances no unsafe operation results.

In one form of the invention, the winding of a code following relay isinterposed in the plate circuit of a preselected one of the electrontubes, and such relay is therefore energized and operated at a ratecorresponding to the code rate at which the two receiving channels arealternately operated.

In another form of the invention, a two-winding polar code followingrelay has one winding included in the plate circuit of one of the twotubes and its other winding in the plate circuit of the other tube andthis relay is operated at a rate corresponding to the code rate at whichthe two receiving channels are alternately operated.

In. still another form of the invention, a primary winding of a decodingtransformer is divided into two portions and one portion is interposedin the plate circuit of one tube and the other portion is interposed inthe plate circuit of the other tube and thus there is induced in thesecondary winding of this transformer an alternating electromotive forceof a frequency corresponding to the rate at which current is alternatelysupplied to the two portions of the primary winding, and in turncorresponding to the rate at which the. two receiving channels arealternately operated. When a code following relay is provided, contactsof the relay are used to control the supply of direct current topreselected portions of the primary winding of the decoding transformerfor inducing in a secondary winding of the transformer an alternatingelectromotive force of a frequency corresponding to the rate at whichthe relay is operated and in turn corresponding to the rate at which thereceiving channels are alternately operated. The secondary winding ofthe decoding transformer is connected to a standard form of decodingmeans and which means ordinarily comprises tuned circuits selectivelyresponsive to the frequency of the electromotive force applied theretoand through which tuned circuits control relays are selectivelyenergized, such control relays being used in turn to govern a multipleposition cab signal or other train governing device.

The connection of each train carried inductor to the associated gridcircuit is made such that the electromotive force picked up by aninductor is of the polarity that will effect the firing of theassociated tube only if it is the proper time for that tube to be firedin the cyclic operation of the two receiving channels. When a codefollowing relay is used we preferably connect the inductors to the' gridcircuits of the respective tubes over contacts of the code followingrelay, the connection of an inductor to the associated grid circuitbeing closed only when the next received electromotive force is the oneto fire the respective tube. This switching of the connections of theinductors serves as an aid in assuring no untimely firing of a tube dueto a stray magnetic field.

' We shall describe three forms of apparatus embodying our invention,and shall then point out the novel features thereof in claims. In theaccompanying drawings. Fig. 1 is a diagrammatic view showing one form ofapparatus embodying our invention when used with train carried traincontrol apparatus. Figs. 2 and 3 are diagrammatic views showing twodifferent modifications of the apparatus of Fig. l and each of whichmodified forms of apparatus also embodies our invention. Figs. 4 and arediagrams illustrating operating characteristics of the apparatus ofFigs. 1 and 2, respectively.

In each of the several views like reference characters are used todesignate similar parts.

Referring to Fig. 1, the reference characters la and lb designate thetrack rails of a stretch of railway over which traflic normally moves inthe direction indicated by an arrow and which rails are formed by theusual insulated rail joints with a track section D-E and which sectionmay be one section of a series of consecutive track sec tions of asignal system. The track section D-E is provided with a track circuitwhich is typical of all sections and which comprises a source of codeddirect current connected across the rails at the exit end of the sectionand a code following relay connected across the rails at the entranceend of the section. In Fig. 1, the source of coded direct current forthe track circuit of section DE comprises a battery I, a codetransmitter or coder CT, 2. track transformer or reactor TD, and

a traffic controlled relay HD. Secondary winding 2 of transformer TB isconnected across the rails at exit end D over wires 3 and I, a currentlimiting resistor 5 being preferably interposed in wire 4. Primarywinding 5 of transformer TD is connected to battery 1 over either codecontact member '!5 or I85 of coder CT according to the position oftraffic controlled relay HD. A condenser E is preferably connectedacross the primary winding 6.

Code transmitter CT may take the form of any one of several well-knownstructures for such devices and it is suflicient to point out that aslong as operating winding 9 of the code transmitter is supplied withcurrent from any convenient source of current, not shown, the codecontact members ?5 and I80 are operated at preselected code rates. Forexample, contact member 15 is operated to engage and disengage a contact15a at the rate of 75 times per minute, and contact member I80 isoperated to engage and disengage a contact l80a at the rate of 180 timesper minute. The relay HD iscontrolled by traffic conditions in advanceof sectionD-E, but such control apparatus is not shown since it would bein accordance with standard practice and forms no part of our presentinvention. It is sufficient for this application to point out that relayHD is picked up to close front contact Hi when the section next in cc ofsection DE is unoccupied and clear traffic conditions prevail, and therelay is released closing back contact ll when the section next in isoccupied and approach traffic conditions prevail. When relay HD ispicked up closing front contact l9, battery 1 is connected to primarywinding 6 over a circuit including contact member L88 of coder CT, andduring each interval that contact l8il-l80a is closed direct currentflows in winding 6 causing magnetic energy to be stored in the magneticcore of transformer TD. The circuit including battery 1, front contacti!) of relay HD and primary winding 6 of transformer TD is soproportioned as to its time constant that the magnetic energy builds uprelatively slow and little, if any, electromotive force is induced insecondary winding 2, at least such electromotive force is so small itcan be neglected. When contact member I80 breaks engagement with contactl80a. the flow of current from battery is interrupted and the magneticenergy stored in transformer TD decays rapidly and an electr .otiveforce of relatively high voltage is induced in secondary winding 2 and acurrent impulse of relatively high peak voltage is supplied to the railsof the section. This impulse of direct current is of a given polarityand is of a short duration. For example, the parts may be proportionedto provide an impulse of current having a duration of the order of say.05 second. Thus, a code impulse of current is supplied to the railseach operation of code contact member I and code impulses of the coderate of impulses per minute are supplied to the rails as long as relayHD is picked up. Under approach tramc conditions, and relay HD isreleased closing back contact ll, battery I is connected to primarywinding 6 over contact member I5 of the code transmitter and theoperation is the same as described above except that the currentimpulses are of the code rate of 75 impulses per minute. Such codeimpulses of rail .current are illustrated in the top series of graphs ofFig. 4, and it is to be observed that the duration of a current impulseis short as compared to the duration between successive impulses. Forexample, if the current impulse is of a duration of the order of .05second as here assumed for illustration, the duration between successiveimpulses of the 180 code rate is of the order of .28 second and theduration between successive impulses of the 75 code rate is of the orderof .75 second. It will be understood, of course, that our invention isnot limited to code rates of 75 and 180 impulses per minute or toimpulses of the duration of the order of .65 second but such code ratesand characteristics for direct current impulses have been foundsatisfactory.

A code following track relay CF is connected across the rails atentrance end E and when section D-E is unoccupied, that is, when thetrain shown conventionally at TV does not occupy the section, relay CFis operated at a code rate corresponding to the code rate of the currentimpulses supplied to the rails through transformer TD in'the manner justexplained. Track relay CF would be used to govern apparatus including acontrol relay for the section next in the rear of section D-E and whichrelay would be similar to control relay HD governed by traffic in thesection in advance of section DE, but such apparatus governed by trackrelay CF is not shown for the sake of simplicity, since, as statedhereinbefore, such control apparatus forms no part of our presentinvention and would be in accordance with standard practice.

The train shown conventionally at IV of Fig. 1 is provided with traincarried apparatus embodying our invention and which apparatus comprisesa'receiving and amplifying means to be shortly described, a codefollowing relay MR, a decoding transformer DT, decoding means DM,control relays A and L and a cab signal CS.

The receiving and amplifying means comprises inductors l2 and i3 andelectron tubes VTl and VT2, inductor l2 and tube VTl being associated toform a first receiving channel, and inductor l3 and tube VT2 beingassociated to form a second receivingchannel. Inductors l2 and I3 arepreferably alike and are mounted on the train ahead of the leading pairof wheels with inductor I2 above rail la and inductor l3 above rail lb.When train TV occupies section D-E and there is no other train betweenit and the exit end of the section an elcctromotive force is induced ineach inductor l2 and IS in response to each code impulse of rail currentsupplied to the rails through track transformer TD in the manriedcurrent source.

ner explained hereinbefore. The effective electromotive force picked upby each inductor I2 and I3 is of a character illustrated by the centerseries of graphs of Fig. 4 and it is to be observed that theelectromotive force picked up by each inductor is of a predeterminedpolarity and of a code rate corresponding to that of the rail current.This is so because each current impulse flows in a predetermineddirection which is opposite for the two rails, and is of the samemagnitude in each rail.

Electron tubes VTI and VT2 are preferably alike and are of the gasfilled grid controlled indirect heater type. Filament I4 of tube VTI isconnected across terminals B32 and N32 of a suitable source of current,such as the usual train carried 32 volt battery or generator, a resistorI5 being included in the heater circuit of tube VTI. Similarly,.fllament I6 of tube VT2 is connected across terminals B32 and N32 witha resistor I'I interposed in the circuit. Consequently, both tubes VT!and VT2 are normally in an active condition.

Tube VTI is provided with a grid circuit that extends from grid I8 overresistor I9, a preselected portion of heater circuit resistor I5 andfilament I4 to cathode 20 of the tube. Tube VT2 is provided with asimilar grid circuit which extends from grid 2| over resistor 22, a.preselected portion of heater circuit resistor I1 and filament I6 tocathode 23. Inductor I2 is connected to the grid circuit of theassociated tube VTI by being connected across resistor l9 over a frontcontact 24 of code following relay MR. As viewed in the drawings, thetop terminal of inductor I2 is connected to the lower terminal ofresistor I3 over wire 25, and the lower terminal of inductor I2 isconnected to the top terminal of resistor I 9 over wire 26, frontcontact 24 of relay MR and wire 21. In like manner, inductor I3 isconnected to the grid circuit of the associated tube VT2 by beingconnected across resistor 22 over a back contact 29 of code followingrelay MR. Again, as viewed in the drawings, the top terminal of inductorI3 is connected to the top terminal of resistor 22 over wire 28 and backcontact 29 of relay MR, and the lower terminal of inductor I3 isconnected to the lower terminal of resistor 22 over wire 30. Each tubeVTI and VT2 is provided with a negative grid bias voltage equal to thevoltage drop across that portion of the heater circuit resistorinterposed in the grid circuit, the value of such negative grid biasvoltage being predetermined by the position of the connection to theheater circuit resistor and can be readily made of a value to normallyavoid firing of the tube. When the electromo-- tive force picked up byinductor I2 or I3, as the case may be, and applied to the grid circuitof the associated tube is of a given polarity it opposes the negativegrid bias voltage and drives the grid in the positive direction by anamount determined by the value of the picked up electromotive force.

Each of the tubes VTI and VT2 is provided with a plate circuit thatincludes a source of direct current, such as a generator; GI, whichgenerator as here shown is the generator of a motor-generator whosemotor element M is driven by current from the B32-N32 train car- To beexplicit, the plate circuit for tube VTI can be traced from the positiveterminal of generator GI over wire 3|, a resistor 32, plate 33 of tubeVTI, intervening tube space to cathode 20, and wire 34 to the negativebefore.

terminal of generator GI. The plate circuit of tube VT2 includes thepositive terminal of generator GI, wire 3|, winding 35 of relay MR,plate 36 of tube VT2, intervening tube space to cathode 23, wires 31 and34, and the negative terminal of generator GI. The voltage of generatorGI and the normal negative grid bias voltage provided for each tube aresuch that each tube is normally non-conductive, but that the change inthe grid voltage effected by the electromotive force of proper polaritypicked up by an inductor causes the tube to be fired, and after whichthegrid loses control due to the nature of the tube and the tube can beextinguished only by a lowering of the plate voltage for an interval atleast equal to the deionization time of the tube.

An extinguishing device is provided which as here shown is a condenserCI connected between plates 33 and 36 of the two tubes, as will beapparent by an inspection of Fig. l. The operation of such extinguishingdevice will appear later.

Relay MR, whose winding 35 is interposed in the plate circuit of tubeVT2, is a code following relay of any one of several well-known types.

. RelayMR controls the supply of direct current to decoding transformerDT in addition to controlling the connections of inductors I2 and I3 tothe respective grid circuits as explained herein- Direct current fromany convenient source, such as the 32 volt train carried source isalternately supplied to two portions of primary winding 38 oftransformer DT over front contact 33 and back contact 40 of relay MR.Hence there is induced in secondary winding 4| of transformer DT analternating electromotive force of a frequency corresponding to the rateat which code following relay MR is operated. Secondary winding M oftransformer DT is connected to the input terminals of a decoding meansshown conventionally at DM. Decoding means DM is preferably of thestandard form and comprises ,tuned circuits to which are connected thetwo control relays A and L. It is suificient for this application topoint out that relay A is efiectively energized and picked up only whenthe alternating electromotive force applied to the decoding means DM isof a frequency corresponding to the code rate for the'rail currentimpulses, and relay L is efiectively energized and picked up in responseto alternating electromotive forces created in response to rail currentof either the 180 or 75 code rate.

Control relays A and L govern the operating circuits of cab signal CS,the arrangement being such that when relay A is picked up closing frontcontact 42, an operating circuit is formed for lamp G and that lamp isilluminated to cause signal CS to display a clear signal indication;when relay A is released closing back contact 43, and relay L is pickedup closing front contact 44, an operating circuit is formed for lamp Yand that lamp is illuminated to cause signal CS to display an approachsignal indication; and when both relays A and L are released closingback contacts 43 and 45, respectively, an operating circuit is formedfor lam-p R, and that lamp is illuminated to cause signal CS to displaya slow speed signal indication.

In describing the operation of the apparatus of Fig. 1, we shall firstconsider that train TV occupies section DE at a time when relay HD ispicked up in response to clear traflic conditions in advance and codeimpulses of the code rate of 180 are supplied to the rails of thesection. Each impulse of rail current induces an electromotive force ineach one of thesinductors l2 and I3. As a starting point, we shau assumethat code following relay MR is released to close back contact 29 andopen front contact 24 so that the connection of inductor l3 to the gridcircuit of tube VTZ is closed but inductor I2 is disconnected from thegrid circuit of tube VTI. Inductor I3 is poled so that the electromotiveforce induced therein due to the impulse of rail current is of apolarity that causes grid 2| to be driven in the positive direction inpotential with respect to cathode 23 and tube VT2 is fired and becomesconductive. Current now flows in the plate circuit of tube V'12 and codefollowing relay MB is energized and picked up. When tube VT2 is thusmade conductive, it remains conductive subsequent to the impulse ofelectromotive force that caused it to be fired until such time as itsplate voltage is reduced. With tube VT! conductive, the condenser Cl ischarged at a potential substantially equal to the voltage drop acrosswinding 35 of relay MR, the left-hand terminal of condenser Cl being thepositive terminal. At the next impulse of rail current the electromotiveforce induced in inductor I2 is applied-to the grid circuit of tube VTIbecause its connection is closed at front contact 24 of relay MR, butthe electromotive force induced in inductor I3 is ineifective becausethe connection of inductor l3'to the grid circuit of tube VT2 is open atback contact 29 of relay MR. Inductor I2 is poled so that thiselectromotive force is of a polarity that causes grid 18 to be driven inthe positive direction in potential with respect to cathode 20 and tubeVTI is fired and becomes conductive. With both tubes conductive,condenser Cl discharges through the two tubes in series and in thedirection that causes cathode 23 of tube VT2. to be positioned withrespect to the plate of that tube, and tube VI2 is immediatelyextinguished. Tube VTI remains conductive subsequent to the terminationof the control electromotive force that caused it to be fired and platecurrent continues to flow with the result that condenser Cl is rechargeddue to the voltage drop across resistor 32, the right-hand terminal ofcondenser Cl being this time positive and the lefthand terminalnegative. When tube VT2 is extinguished code following relay MB isdeenergized and released to close back contact 29 and open front contact24 so that at the next impulse of rail current the electromotive forceinduced in inductor I3 is effective to cause tube VT2 to be fired andthe electromotive force picked up by inductor I3 is inefiective. firedcondenser CI discharges through the tubes in series, the discharge beingthis time in a direction that causes cathode 29 of tube VTI to berpositive with respect to the plate of that tube,

picked up due to the flow of plate current of tube VTZ and on picking upserves to switch the connections of inductors l2 and I3. Such alternateoperation of the two receiving channels is continued as long as thetrain occupies the section and code impulses of direct current areapplied to the track rails. Relay MR is thus operated at a ratecorresponding to the code rate at which the two receiving channels arealternately operated and in turn at a rate corresponding to the coderate of the rail current. Operation of relay MR causes direct current tobe alternately supplied to the two portions of primary winding 38 Whentube VTZ is secondary winding ll an alternating electromotive force of acorresponding frequency. The operating characteristics of relay MR areillustrated by the bottom series of graphs of Fig. 4, and it is to bepointed out that the relay is operated at substantially equal on and ofiperiods notwithstanding the fact that the duration of the on periods ofthe rail current is short as compared to the duration of the offperiods.

Operation of relay MR to thus create an alternating electromotive forcein the decoding transformer causes relay A to be energized and picked updue to the frequency of such'alternating electromotive force, and relayA on being picked up causes signal CS to display a clear signalindication.

in the event relay HD is released due to'approach trafiic conditions inadvance and current impulses or the code rate are supplied to the railsof sections DE at a time the section is occupied by train TV, the traincarried apparatus is operated in a manner similar to that effected underclear trafiic conditions except for the fact that the receiving channelsare now alternately operated at the '15 code rate causing relay MR to beoperated at a. corresponding rate, and which rate or operation of relayMR in turn causes the alternating electromotive iorces created in thedecoding transformer DT to be of a frequency that results in relay Lbeing picked up and relay A being released. This set up of the controlrelays A and L causes signal CS to display an approach signalindication.

1n the event section DE is occupied by another train ahead of train TV,then the rail current; is shunted by the leading train and the apparatusof train TV is inactive and both relays A and L are released to causesignal CS to display a slow speed signal indication.

Referring to Fig. 2, the track rails in. and lb of a stretch of railwayare formed with a track section DE which is provided with a trackcircuit the same as in Fig. 1. In Fig. 2, the means for supplying codeddirect current to the rails at exit end D of the section comprisesbattery 1, code transmitter CT, a code repeater relay CP and trafficcontrolled relay H1), relay HD being governed by trafiic conditions inadvance and code transmitter CT being operated to actuate contactmembers 15 and I the same as in Fig. 1. When relay HD of Fig. 2 ispicked up closing front contact l0, code repeater relay CP is energizedover a circuit including terminal B of a convenient source of current,such as a battery not shown, front contact ID of relay BB, code contactmember I80 of code transmitter CT, winding of relay CP, and terminal Cof the same source of current. It follows that repeater re-' lay CP ispicked up and released in step with the operation of code contact memberI80. Relay CP when picked up to close front contact 46 completes theconnection of battery I to the rails, and when the relay is releasedbattery 1 is disconnected from the rails and the rails are shortcircuited through a path including back contact 41. Hence, during eachoperation cycle of ontact member I80, direct current is supplied to oftransformer DT so that there is induced in 75 the rails forsubstantially one-half of the cycle and the current is interrupted forsubstantially one-half of the cycle. The top series of graphs of Fig. 5illustrates such coding of the rail current, the raised portions of Fig.5 illustrating the on periods when current flows in the rails and thedepressed portion illustrating the off periods when no current flows.with relay I-lD released closing back contact II, repeater relay CP iscontrolled over code contact member I and the operation of coding thecurrent supplied to the rails is substantially the same as before exceptfor the fact that the coding is now of the 75 code rate.

Code following track relay CF of Fig. 2 is operated by the coded directcurrent supplied to the rails at the exit end D in substantially thesame manner as explained in connection with Fig. 1 and relay CF would beused to control wayside signals and other apparatus the same as in Fig.l.

The train carried apparatus for train TV of Fig. 2 comprises atwo-channel receiving and amplifying means and a standard form ofdeccding and signaling means that are the same as in Fig. 1, except thatresistor 32 interposed in the plate circuit of tube VTI and codefollowing relay MR interposed in the plate circuit of tube VT2 of Fig. 1are replaced by a two-winding polar code following relay MRI whose topwinding 48 is interposed in the plate circuit of tube VTI and whoselower winding 49 is interposed in the plate circuit of tube VT2. It isbelieved that the train carried apparatus of Fig. 2 can best beunderstood from a description of its apparatus when taken in connectionwith the detailed description of the train carried apparatus of Fig. 1.

In describing the operation of the apparatus of Fig. 2, we shall firstconsider the operating 1 steps when train TV occupies the section D-Ewith relay HD picked up because of clear trafilc conditions and directcurrent of the 180 code rate is supplied to the rails. At the start ofan on code period and current builds up in the rails, an electromotiveforce is induced in each inductor I2 and I3, the polarity of suchelectromotive forces being predetermined according to the direction thecurrent is made to flow in the rails. We shall assume that at thetimethese electromotive forces are thus induced in inductors I2 and I3,the code following relay MRI occupies its right-hand position asillustrated by the solid lines for contact members 50, 5| and 52 of therelay. At the right-hand position of relay MRI the connection ofinductor I3 to the grid circuit of tube VT2 is closed at the right-handpolar contact of contact member 50, but the connection of inductor I2 tothe grid circuit of tube VTI is opened at contact member 5|.Consequently, the electromotive force induced in inductor I3 is appliedto the tube VT2, but the electromotive force induced in inductor I2 isineffective.

Inductor I3 is poled so that the polarity of the electromotive forceinduced therein due to the building up of rail current is such as todrive grid 2| of tube VT2 in the positive direction in potential withrespect to cathode 23 and tube VT2 is fired and becomes conductive.Plate circuit current flows through tube VT2 and energizes winding 43 ofCondenser CI is charged due to the voltage drop across winding 49, itsleft-hand terminal being the positive terminal. At the end of this oncode period of the rail current and the current dies away, anotherelectromotive force is induced in each of the inductors I2 and I3. Foreach inductor, the polarity of such electromotive force is opposite tothat of the electromotive forces picked up when the current builds up atthe start of the on code period. The electromotive force induced ininductor I2 at the end of an on code period is applied to tube VTIbecause contact member 5I engages a left-hand polar contact but theelectromotive force induced in inductor I3 is ineffective because theconnection of that inductor is now open. Inductor I2 is poled so thatthe polarity of the electromotive force picked up due to the dying awayof rail current drives the grid I8 of tubev VTI in the positivedirection in potential with respect to cathode 20 and the tube is firedand made conductive. Condenser CI now discharges through the tubes inseries to extinguish tube VT2. The plate circuit current for tube VTIflowing in winding 48 of relay MRI energizes the relay at a polaritythat operates the contact members 50, 5| and 52 back to the righthandposition. Also this plate current flowing in tube VTI rechargescondenser CI, the righthand terminal being the positive terminal. At thestart of the next on code period of rail current, the electromotiveforces picked up by inductors I2 and I3 are of the polarity explained inconnection with the start of the first on code period and theelectromotive force picked up by inductor I3 is efiective to cause tubeVT2 to be fired which results in operation of relay MRI to its left-handposition. Condenser CI now discharges through the tubes in series toextinguish tube VTI, and is then recharged due to the plate circuitcurrent for tube VT2. The above described alternate operation of the tworeceiving channels of Fig. 2 and in turn operation of code followingrelay MRI is repeated as long as the train TV remains in section D-E andcoded direct current is supplied to the track rails. The electromotiveforces picked up at the start and at the end of each on code period areillustrated by the center series of graphs of Fig. 5, and the operationof relay MRI is illustrated by the bottom series of graphs of Fig. 5.

Code following relay MRI at its contact member 52 controls the supply ofdirect current to the two portions of primary winding 38 of decodingtransformer DT and there is induced in secondary winding 4| analternating electromotive force of a frequency corresponding to the rateat which relay MRI is operated and under clear traffic conditions thealternating electromotive force induced in secondary winding 4| is of afrequency corresponding to the 180 code rate of the rail current. Thiselectromotive force induced in secondary winding M when applied to thedecoding means DM energizes relay A and causes signal CS to display aclear signal indication.

In the event train TV of Fig. 2 occupies the section DE under approachtraffic conditions and the current is coded at the 75 code rate, theoperation of the apparatus is the same as described in connection withcurrent of the 180 code rate except for the rate at which relay .MRI isoperated and this time the alternating electromotive force created inthe decoding transformer is of a frequency that causes relay L to bepicked up and relay A to be released so that signal CS displays anapproach signal indication. Also in connection with Fig. 2, if a trainahead of th train TV shunts the rail current, the train carriedapparatus of train TV is inactive and a slow speed cab signalindicationis displayed.

Referring to Figs. 4 and 5, it is to be observed that the code followingrelay MRI of Fig. 2 is operated at a rate twice that of code followingrelay MR of Fig. 1. This means that the tuned circuits of the decodingmeans DM would be adjusted for the particular rate at. which therespective code following relay is operated.

In' connection with Fig. 2, it is to be pointed out that while inductorsl2 and I3 are made alternately effective and ineffective by the controlof their connections by the code following relay MRI, such control bythe code following relay may not be required and alternate operation ofthe receiving channels would be effected with such control of the codefollowing relay omitted. For example, the electromotive force picked upby inductor B at the start of each on code period is of a polarity thatwill cause tube VTZ to be fired. whereas the polarity of theelectromotive force induced in inductor l3 at the end of each on codeperiod is opposite and is of a polarity that drives grid 23 morenegative in potential with respect to the cathode and hence would notserve to cause the tube to fire. Similarly, the electromotive forcecreated in inductor I2 at the end of each on code period is of apolarity that causes tube VI! to be fired whereas the polarity of theelectromotive force created at the start of the on code period of therail current tends to drive grid [8 of tube VTI more negative inpotential with respect to the cathode of the tube.

Referring to Fig. 3, the track apparatus for track section D-E is thesame as in Fig. 2 and the description thereof need not be repeatedexcept to point out that the direct current is coded in the mannerillustrated by the top series of graphs of Fig. 5.

The train carried apparatus provided for train TV of Fig. 3 comprisestwo receiving channels together with standard decoding and signalingmeans the same as in Fig. 1, except resistor 32, code following relay MRand decoding transformer DT of Fig. 1 are replaced by a decodingtransformer DTI. One portion of primary winding 53 of transformer DTI isinterposed in the plate circuit of tube VT! and a second portion ofprimary winding 53 is interposed in the plate circuit of tube VT2. It isbelieved that the apparatus of Fig. 3 will best be understood from adescription of its operation taken in connection with the description ofthe apparatus of the train TV of Fig. 1.

In describing the operation of the apparatus of Fig. 3 we shall firsttake up the operating steps efiected when train TV occupies section D-Eunder clear trailic conditions and current coded at the 180 code rate 3supplied to the rails. When current builds up in the rails at the startof an on code period, an electromotive force is induced in each inductorl2 and I3. Inductor l3 which is connected to the grid circuit of tubeVT2, is poled so that the electromotive force picked up by inductor l3due to the building up of rail current is of a polarity such as to drivegrid 2| of tube VT! in the positive direction and cause that tube to befired. Inductor H which is connected to the grid circuit of tube VTI, ispoled so that the electromotive force picked up by inductor l2 due tothe building up of rail current is of a polarity to drive the grid oftube V'I'l more negative in potential with respect to the cathodeandtube VTI remains extinguished. The plate current flowing when tubeVT! is made conductive energim the right-hand portion of primary winding53 of transformer VT! and also causes condenser CI to be charged in themanner explained hereinbefore, the lefthand terminal of condenser Clbeing the positive terminal. At the end of the on period of the railcurrent an electromotive force is induced in each of inductors l2 and I3as the current dies away, the polarity of each such electromotive forcebeing opposite to that created at the beginning of the on code period.This time the electromotive force of inductor I2 is of a polarity thatcauses tube VTI to be fired, while the electromotive force of inductorI3 is of a polarity that drives the grid of tube VT! in the negativedirection. With both tubes fired, condenser Cl discharges to extinguishtube VT2 and the plate current flowing in tube VTI energizes theleft-hand portion of primary winding 53 of transformer DI! and chargescondenser Cl with its right-hand terminal the positive terminal. At thenext on period of the rail current, the tubes are alternately fired,tube VT2 being fired at the beginning of the on period and tube VTIbeing fired at the end of the on period. Such alternate operation of thereceiving channels of Fig. 3 causes an alternating electromotive forceto be created in secondary winding 54 of transformer DTI which has afrequency corresponding to the code rate at which the receiving channelsare alternately operated. Secondary winding 54 is connected to theinput; side of the decoding means DM causing thereby control relay A tobe picked up and signal CS to display a clear signal indication inresponse to the code rate for the rail current.

Under approach trafilc conditions for the apparatus of Fig. 3, theoperation is the same as explained for clear traffic conditions exceptthe receiving channels are now alternately operated at the '75 code ratewith the result that control relay L is picked up and relay A isreleased causing signal CS to display an approach signal indication.Furthermore, when section D-E is occupied by another train ahead oftrain TV the train carried apparatus of train TV is inactive and a slowspeed signal indication is displayed. In connection with Fig. 3, it isto be observed that the two tubes serve as a code following relay andtheir plate circuit currents are used to energize the decodingtransformer.

Apparatus herein described has the advantages that direct current can beused to assure eifective broken rail protection for long track sections,the train carried receiving and amplifying means is effectivelyresponsive to a relatively low energy of rail current so that a savingin the output of the track battery is obtained and substantially equalon and oif periods are obtained for control of the standard decodingmeans, notwithstanding unequal on and off periods of the coded railcurrent may exit due either to the form of coding employed or to codedistortion. Furthermore, false energization of the train carriedreceiving means by stray magnetic fields, such as magnetized rail spotsis avoided.

Although we have herein shown and described but three forms of railwaytraihc controlling apparatus embodying our invention, it is understoodthat various changes and modifications may be made therein within thescope of the appended claims without departing from the spirit and scopeof our invention.

Having thus described our invention, what we claim is:

1. In combination, a track section, a train to travel such section,means connected to the rails of said section to supply to the railsdirect current coded at a preselected code rate; two train carriedreceiving channels each of which includes an inductor, a gas filled tubeand a circuit connection to connect the inductor to the grid of thetube; said tubes each provided with a plate circuit which includes asource of direct current of a voltage normally ineffective to fire therespective tube, said inductors mounted one in inductive relation to onerail and the other in inductive relation to the other rail for eachinductor to pick up an electromotive force in response to said codedrail current, said circuit connections arranged for said electromotiveforces picked up by said inductors to alternately fire the tubes, meansincluding a condenser connected across the plates or said tubes toalternately extinguish said tubes, and signaling means coupled to theplate circuit of at least one of said tubes controlled by the currentthus caused to recurrently fiow in the plate circuit of said one tube.

2. In combination, a track section, a train to travel such section,trackway means to supply to the rails of said section direct currentcoded at a predetermined code rate, two train carried receiving channelseach of which includes an inductor and a gas filled tube with eachinductor provided with a connection to the grid circuit of the tube ofthe same channel, said inductors one mounted above one rail and theother mounted above the other rail for each inductor to pick up anelectromotive force due' to said coded rail current, said tubes eachprovided with a plate circuit including a source of direct current whichis normally ineffective to fire the respective tube, said inductorconnections arranged to alternately fire said tubes by the electromotiveforces picked up by the inductors, means including reactance connectedacross the plates of said tubes to alternately extinguish the tubes, andtrain carried signaling means coupled to the plate circuit of at leastone of said tubes and controlled by the current thus caused torecurrently flow in the plate circuit of said one tube.

3. In combination, a track section, a train to travel said section,trackway means connected across the rails of the section to supply tothe rails direct current coded at a preselected code rate, two receivingchannels mounted on said train and each including an inductor and a gasfilled tube, said inductors one mounted over one rail and the othermounted over the other rail for each inductor to receive anelectromotive force in response to said coded rail current, said tubeseach provided with a grid circuit to which the inductor of the samechannel is connected, said tubes each provided with a plate circuitwhich includes a source of direct current of a voltage inefiective tonormally fire the tube, said grid circuits arranged in their connectionsto the respective inductors to alternately fire the tubes in response tosaid received electromotive forces, means including a condenserconnected across the plates of said tubes to alternately extinguish saidtubes, and train carried signaling means electrically associated withsaid receiving channels and controlled by such altern te Operation ofthe channels in response to said coded rail current.

4. In combination, a track section, a train to travel such section,means connected to the rails of said section to supply to the rails timespaced impulses of direct current, two inductors mounted on said trainwith one inductor above one rail and the other inductor above the otherrail for each of said inductors to receive time spaced electromotiveforces due to said rail current, two gas filled tubes on said train, aplate circuit for each of said tubes and each said plate circuitincluding a source of direct current of a voltage insufiicient tonormally fire the respective tube, a first grid circuit means for one ofsaid tubes and including said one ind'uctor and a second grid circuitmeans for the other one of said tubes and including said other inductor,said grid circuit means provided with a predetermined relationship toalternately fire said tubes in response to said time spacedelectromotive forces received by said inductors, means including acondenser connected across the plates of said tubes to alternatelyextinguish said tubes, and signaling means on the train electricallyassociated with said plate circuits and controlled by the currents thuscaused to alternately fiow in the plate circuits.

5. In combination, a track section, a train to travel such section,means connected across the rails to supply coded direct current thatflows in the rails in series, two train carried inductors one mountedover one rail and the other mounted over the other rail for eachinductor to receive energy in response to said coded direct current, twotrain carried gas filled tubes, a heater circuit including a resistorfor each of said tubes, 3, plate circuit including a source of directcurrent for eacn of said tubes, a grid circuit for each of said tubesand each grid circuit including at least a portion of the resistor ofthe heater circuit of the same tube to provide a negative grid biasvoltage sufllcient to normally retain the tube extinguished, a firstcircuit connection to connect a selected one of said inductors to thegrid circuit of a selected one of said tubes to apply to said one tubethe energy received by said one inductor, a second circuit connection toconnect the other one of said inductors to the grid circuit of the otherone of said tubes to apply to said other tube the energy received bysaid other inductor, said first and second circuit connections providedwith a predetermined relationship to alternately fire said tubes by saidreceived energy, means including a condenser connected across the platesof said tubes to alternately extinguish the tubes, and train carriedsignaling means electrically coupled to the plate circuit of at leastone of said tubes and controlled by such altemate operation of thetubes.

6. In combination, a track section, a train to travel such section,means connected to the rails of the section to supply direct currentcoded to have alternate on and ofi periods, two receiving channels onsaid train each of which channels includes an inductor and a gas filledtube together with a circuit connection to connect the inductor to thegrid of the tube, said inductors mounted on the train one over one railand the other over the other rail for each inductor to pick up anelectromotive force at the start and at the end of each on code periodof said rail current, a plate circuit including a direct current sourcefor each of said tubes and which direct current source is normallyinefiective to fire the respective tube, said inductors oppositely poledto fire a selected one of the tubes by the electromotive force picked upat the start of an on code period and to fire the other tube by theelectromotive force picked up at the end of an on code period, meansincluding a condenser connected to said plate circuits to alternatelyextinguish said tubes, and train carried signaling means coupled to theplate circuit of at least one of said tubes and controlled by suchalternate operation of said tubes.

7. In combination, a track section, a train to travel such section,means connected to the rails of the section to supply coded directcurrent, two receiving channels on the train and each of which channelsincludes a grid controlled gas filled tube and an inductor connected tothe grid of the tube, said inductors disposed one over one rail and theother over the other rail for each inductor to receive energy of a codecorresponding to said coded direct current, a plate circuit for each ofsaid tubes and which plate circuits have a common source of directcurrent that is normally inefiective to fire the tubes, a code followingrelay having a winding interposed in the plate circuit of at least oneof said tubes, contacts of said relay interposed in said receivingchannels to alternately close the connections of said inductors foralternately firing said tubes in response to said received energy, meansincluding a condenser connected to the plates of said tubes toalternately extinguish said tubes, and signaling means on the traincontrolled by said relay and efiectively energized by the operation ofsaid relay due to the alternate operation of the tubes.

8. In combination, a track section, a train to travel such section,means connected to the rails of the section to supply coded directcurrent, two receiving channels on the train each of which channelsincludes an inductor and a grid controlled gas filled tube together witha circuit connection to connect the inductor to the grid of the tube,said inductors mounted on the train one over one rail and the other overthe other rail for each inductor to pick up an electromotive force of acode corresponding to' that of said coded direct current, a platecircuit for each of said tubes, 9. source of direct current interposedin each of said plate circuits but normally ineffective to fire thetubes, a code following relay operable to a first and a second positionand having a winding interposed in the plate circuit of a preselectedone of said tubes to operate the relay by the plate current of thattube, a first position contact of said relay interposed in the circuitconnection of the channel including said one tube and a second positioncontact of the relay interposed in the circuit connection of the channelincluding the other tube to alternately fire the tubes by said picked upelectromotive forces, means including a condenser connected to theplates of said tubes to alternately extinguish the tubes to operate therelay according to code of said coded direct current, and train carriedsignaling means controlled by the relay when thus operated.

9. In combination, a track section, a train to travel such section,means connected to the rails of the section to supply direct currentcoded to form alternate on and ofi periods, two receiving channels onsaid train each of which channels includes an inductor and a gridcontrolled gas filled tube together with a circuit connection to connectthe inductor to the grid of the tube, said inductors mounted on thetrain one over one rail and the other over the other rail for eachinductor to pick up an electromotive force at the start and at the endof each on code period of said rail current, a plate circuit for each ofsaid tubes, at common source of direct current for said plate circuitsbut of a voltage insufllcient to normally fire the tubes, 9. codefollowing relay having a winding interposed in the plate circuit of atleast one of said tubes for energizing the relay by the plate circuitcurrent of said one tube, a first contact of said relay interposed inthe circuit connection of one of said channels and a second contact ofthe relay interposed in the circuit connection of the other one of saidchannels to permit one tube to be fired in response to the electromotiveforce picked up at the start of each on code period only and the othertube to be fired in response to the electromotive force picked up at theend of each on code period only, and signaling means controlled by saidrelay.

10. In combination, a track section, a train to travel such section,means connected to the rails of the section to supply direct currentcoded to form alternate on and off periods, two receiving channels onsaid train each of which channels includes an inductor and a gridcontrolled gas filled tube together with a circuit connection to connectthe inductor to the grid of the tube, said inductors mounted on thetrain one over one rail and the other over the other rail for eachinductor to pick up an electromotive force at the start and at the endof each on code period of said rail current, a plate circuit for each ofsaid tubes, a common source of direct current for said plate circuitsbut of a voltage insufiicient to nor mally fire the tubes, 9. twowinding polar relay one of which windings is interposed in the platecircuit of one tube and the other winding interposed in the platecircuit of the other tube, a normal polar contact of said relayinterposed in the circuit connection of one of said channels and areverse polar contact of the relay interposed in the circuit connectionof the other channel to alternately connect said inductors to the gridsof the respective tubes for alternately firing said tubes in response tosaid picked up electromotive forces, and signaling means controlled bysaid relay. I

11. In combination, a track section, a train to travel such section,means connected to the rails of the section to supply impulses of directcurrent of a preselected code rate and which impulses are of shortduration compared to the duration between successive impulses, tworeceiving channels on said train and each of which channels includes agrid controlled gas filled tube and an rnotive force of l a codecorresponding to that of the rail current, a plate circuit for eachtube, a common source of direct current for said plate circuit but of avoltage insuflicient to normally fire the tubes, a code following relayhaving a winding interposed in a preselected one of said plate circuitsto energize the relay when the associated tube is fired, a back contactof said relay interposed in the inductor connection of one channel and afront contact of the relay interposed in the inductor connection of theother channel to alternately fire the tubes in response to said pickedup electromotive forces, means including a condenser connected acrossthe plates of said tubes to alternately extinguish the tubes to operatethe relay at a rate corresponding to said preselected code rate and withsubstantially equal energized and deenergized periods, and signalingmeans responsive to current of a frequency corresponding to said coderate controlled over contacts of said relay.

12. In combination, a track section, a train to travel such section,means connected to the rails or the section to supply thereto codeddirect current having alternate on and ofl periods, two train carriedinductors one mounted over each rail to receive an electromotive forceof a code corresponding to that of the rail current, two train carriedgas filled tubes, a plate circuit for each of said tubes, a grid circuitfor one of said tubes and including a source of negative grid biasvoltage and a selected one of said inductors and which inductor is poledto drive the grid more positive by the electromotive force received atthe start of each on code period and cause the tube to fire; a gridcircuit for the other one of said tubes and including a source ofnegative grid bias voltage and the other one of said inductors and whichinductor is poled to drive the grid more positive by the electromotiveforce received at the end of each on code period and cause the tube tofire, a condenser connected across the plates of said tubes toalternately extinguish the tubes to cause plate current to fiow in theplate circuit of said one tube each on code period and plate current tofiow inthe plate circuit of the said other tube ,each ofi code period,and signaling means coupled to the plate circuit of at least one ofsaid-tubes and controlled by such alternate operation of said tubes.

13. In combination, a track section, a train to travel such section,means connected to the rails of the section to supply thereto codeddirect current having alternate on and ofi periods, two train carriedinductors one mounted over each rail for each inductor to inductivelyreceive an electromotive force of a code corresponding to that of therail current, two train carried gas filled tubes, a plate circuit foreach tube each of which plate circuits includes a direct current sourceand a winding, a grid circuit for each tube and each of which gridcircuits includes a resistor and a source or voltage efiective to applya predetermined negative grid bias voltage to normally retain the tubeextinguished, one of said inductors connected across the grid circuitresistor of one of the tubes to fire that tube by the electromotiveforce received at the start of each on code period of the rail current,the other one of said inductors connected across the grid circuitresistor of the other tube to fire that tube by the electromotive forcereceived at the end of the on code period of the rail current, acondenser connected across the plates of said tubes to alternatelyextinguish the tubes, and signaling means efiectively energized by thecurrent thus caused to alternately flow in said plate circuit windings.

14. In combination, a track section, a train to travel such section,means connected across the rails of the section to supply time spacedimpulses of current, two train carried inductors one mounted over eachrail to inductively receive time spaced electromotive forces in responseto said rail current, two train carried gas filled tubes, a platecircuit for each of said tubes including a source of direct current, aheater circuit for each of said tubes including a resistor, a gridcircuit for each of said tubes ineluding at least a portion of theresistor of the heater circuit oi! the same tube to provide a negativegrid bias voltage for normally retaining the tube extinguished, one ofsaid inductors connected across the grid and cathode of one of the tubesand the other inductor connected across the grid and cathode of theother tube to apply to the tubes said received electromotive forces,said inductors poled so that the grid of one of said tubes is driven inthe positive direction and the tube fired by the electromotive forcereceived when the rail current impulse builds up and the grid of theother tube is driven in the positive direction and the tube fired by theelectromotive force received when the rail current impulse dies away, acondenser connected across the plates of said tubes to alternatelyextinguish the tubes, and signaling means coupled to said plate circuitsand effectively energized by the currents thus caused to alternatelyflow in the two plate circuits.

15. In combination, a track section, a train to travel such section,means connected across the rails of the section to supply coded directcurrent having alternate on and oil periods, two inductors on the trainone over each rail for each inductor to receive an electromotive forceat the start and at the end of each on period of such rail current, twogrid controlled gas filled tubes and a decoding transformer on thetrain, a plate circuit for each tube and each of which plate circuitsincludes a preselected portion of a primary winding of said transformer,

a train carried source of direct current interposed in each of saidplate circuits but normally inefl'ective to fire the tubes, one or saidinductors connected across the grid and cathode of one of said tubes andpoled to apply a positive voltage to the grid due to the electromotiveforce received at the start of each on period of rail current and firethe tube, the other inductor connected across the grid and cathode ofthe other tube and poled to apply a positive voltage to the grid due tothe electromotive force received at the end of each on period of therail current and fire the tube, means including a condenser connectedacross the plates of said tubes to alternately extinguish the tubes, andtrain carried signaling means connected to a secondary winding of saidtransformer and effectively controlled by the alternating electromotiveforce induced in the secondary winding due to the direct current causedto alternately fiow in said portions of said primary winding by suchalternate operation of said tubes.

' ARBA G. WILLIAMSON.

ARBA G. WILLIAMSON, JR.

